What is this feature? (Reavis North / Reavis Falls)

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Every time I hike to Reavis from the North, I look out from Castle Dome and see a geological feature at 33.539624, -111.190147 (Lat, long). I've looked at in binoculars and figured it was a landslide, which is also what it looks like in the satellite view. However, I don't know of comparable landslides in the area, so maybe it's something else. This has always bugged me and I wonder why nobody ever mentions it. Any ideas?

[joebartels]

looks like a big sink hole/slide
http://hikearizona.com/map.php?QX=1162

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@joe bartels Yes, that's the spot. I was surprised that it looks so gravelly and poorly consolidated.

[Al_HikesAZ]

@teva joe Yes, that's the spot. I was surprised that it looks so gravelly and poorly consolidated.

A volcanic anomaly? A rockalanche?

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A volcanic anomaly?

It seems that way to me. It would make sense for a cinder pile, but I don't recall that sort of thing. There's welded tuff in that area and more generally massive stuff, but I suppose there could have been enough erosion to create a thick layer of small stuff.

[hippiepunkpirate]

Anybody have a photo?

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Anybody have a photo?

I don't have anything as good as zooming in about three more notches on the satellite view in Joe's link.
http://hikearizona.com/map.php?QX=1162

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Huh, I actually do have a decent photo. I scaled it way down for posting. If the resolution isn't good enough, I can make a better one.

[hippiepunkpirate]

I'd say with relative certainty, that is a landslide. The scarp is almost like something you would see in a geology diagram... http://nationalatlas.gov/articles/geolo ... e.html#one

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@hippiepunkpirate Thanks for the confirmation. Some other key elements pictured in that diagram are also visible. I'm still struggling to understand the nature of that material. Is it erosional debris from the nearby higher and rockier places, did it crumble from weathering in place, or was is never consolidated to begin with?

[joebartels]

Calson is going to ask around, keep his ears open, if anyone has anymore info.

Charles Lui reported the collapse of the rim at Reavis Falls in 2004, so maybe some of that terrain is not stable.

on a slightly related note...
a little plug for this years "Dutch Hunters' Rendezvous"
- October 21, 22, & 23
- no admission, no charge for camping, and all activities are free, based on first come, first served
- bring a chair
http://superstitionmountaintomkollenbor ... zvous.html

The 7th annual Dutch Hunter rendezvous is scheduled for October 21st, 22nd and 23rd at the Dons camp just off Peralta road on the 110th anniversary of Jacob Waltz's death. Our Guest speaker for Saturday night this year is our good friend Bob Schoose. The gate to the camp should be open Thursday afternoon for our out of town guests and other early arrivals. Remember there is no water available at the site, but there are rest rooms on site. All fires must be contained and horses should be kept in the upper camp area adjacent to the entry gate. We have several special guests making their first trip to the rendezvous including Ernie Provence and another guest making his return to the Superstitions for the first time in 45 years.

[hippiepunkpirate]

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Yeah, you got me stumped. I searched the AZ Geological Survey Repository Docs...they have a few geologic maps for the Supes, but none that cover that portion of the Pinyon Mountain quad. Google searches come back with nothing. Anybody know any geologists that are experts on the Supes? Unfortunately all my geology connections are at NAU...which tends to specialize in Flag area volcanics, the Colorado Plateau, and the Verde Valley/Mogollon Rim. It would be fun to go take a look first hand, not sure if answers would be obvious without a highly knowledgeable geologist in tow (I don't think my geology minor qualifies me).

Going off what little information we have, I'll take a WAG:
One thing I do find interesting is that it is located on a hillside above Lime Mountain. The names of such things are often deceiving (such as Marble Canyon was named as such because of the Redwall Limestone, which Powell assumed to be marble, which forms when limestone is subjected to low grade metamorphism), but I do wonder if there is some sort of calcium carbonate based rock (limestone, marble, ect) in that area that could be slowly dissolving due to groundwater flow (notice Lime Mountain Spring directly downhill from the slide) and may have contributed to loosening the bedrock to the extent that a landslide might occur during some sort of extreme rain event. To me, the likelihood of finding limestone or similar rocks in the heart of the range seems slim, but being that volcanic mechanism that created the range shut off approximately 15 million years ago, perhaps erosion in that area of the range has partially exposed underlying rocks, such as the Mescal Limestone, which is present on the fringes of range (I spotted it on the Goldfield Mtns quad geologic map on a isolated hillside near the Peralta Rd). From what little I've read about Supes geology, it does seem this area is outside the main complex of the volcanic calderas that created the range (see this link for a map, the Reavis area looks to be outside what they call the "Tortilla Caldera": http://www.gemland.com/def33.htm). Based on the location of these calderas, I would imagine that the tuffs and rhyolites in the Reavis area would be smaller in thickness than in the "core" of the calderas, which I would expect to make it reasonable for 15 million years of erosion to expose underlying rocks. That's my best guess at this point...who knows if I'm right or wrong, but it was a ton of fun to think about!

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@hippiepunkpirate Thanks for putting your mind to it. I've always thought that Lime Mountain was incorrectly named, especially since everything at lower elevations near there is volcanic, but perhaps it's a relic of something that stuck up. Maybe this is enough reason for a little side trip. I have found other, older stuff south of the ranch (near the Rogers trail intersection), including a big hunk of schist (another head-scratcher) that many others have probably noticed, too.

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Calson is going to ask around, keep his ears open, if anyone has anymore info.

It would be cool if he turned something up. I wondered if it might be somewhat recent, since the margins remain so crisp. However, with such little rainfall the change would happen slowly.

[joebartels]

Here is Kollenborn's reply to Carlson...

I have inspected it a couple of times over the years Jack. My personal opinion is the depression is caused soil consolidation due to a very wet period. I would suggest it is possible solifluction or soil creep. This is a condition is applied to slow imperceptible slowing from higher to lower ground of masses of rock or soil saturated with water during an extremely wet winter or spring. If an underlying strata contains clay you could have massive movement. Snow or heavy rains could bring this condition about. I am basing this on my geology training and experience from college at ASU. My personal inspection of the area; Jack is indicative of solifluction or soil creep. Of course it could be something else. One needs core samples to be positive.
- Kollenborn

This geology stuff is over my head! If you disagree, please do so with tact as these legends have kindly enriched so many of our lives.

[PLC92084]

My (very limited) expertise leads me to think this isn't soil creep. More likely unstable strata induced to failure through the introduction of excessive moisture or localized geologic forces. I'm just speculating; don't mean to imply any expertise (other than courses I've taken in geology waaaaay back in college...).

What does the local historical geology indicate for this area?

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Thanks for passing that along!

If an underlying strata contains clay you could have massive movement.

Now that's an interesting idea. There could be a paleosol under the volcanics. I don't know if it has been documented in that area and it's not what I would expect, but it could be even just a bit of more weathered volcanics. It's cool that such an eminent Supes guy found it interesting enough for a detour.

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What does the local historical geology indicate for this area?

Tertiary and quaternary volcanics. There's some older stuff further east.

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This geology stuff is over my head!

C'mon Joe, join the crowd! One of the great things about AZ is that it has so much geology running around naked. It has inspired me to learn as much as I can and pester my geologist relatives with thousands of questions. They'll be happy to know that I'm pestering somebody else.

[hippiepunkpirate]

One needs core samples to be positive.

I agree with this, as I think knowing what is under the ground there is the key understanding this feature. For soil creep to occur in the bedrock (and that is a huge mass that most certainly includes bedrock), the bedrock would have to be a relative weak or broken (or both) rock layer. The mention of clay, and Alex's further elaboration of a possible paleosol (which is an ancient layer of soil that got covered by a rock layer, usually a lava flow) is an interesting idea, and sounds best possible explanation.